1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to the measurement of wireless network apparatuses, and control of the transmission rate using the same. More particularly, the present invention relates to a wireless network apparatus and a method for controlling the transmission rate using the same, whereby a receiver side is capable of constantly maintaining the maximum transmission rate by coordinating the maximum number of packets to be sent to the network from a sender side.
2. Description of the Related Art
As illustrated in FIG. 1, a wireless network apparatus according to a conventional art comprises a packet sending device 10 to send a packet, and a packet receiving device 20 to receive the sent packet and send a response packet to the packet sending device 10 depending upon whether there are any errors in the received packet.
The packet sending device 10 comprises a packet sending unit 11 to send a packet to the packet receiving device 20, a response packet receiving unit 12 to receive a response packet, and a packet determining unit 13 to determine a packet to be sent according to the received response packet.
The packet receiving device 20 comprises a packet receiving unit 21 to receive a packet, a packet error detecting unit 22 to detect an error in the received packet, a response packet generating unit 23 to generate a response (packet) to the received packet, a response packet sending unit 24 to send the generated response packet to the packet sending device 10, a data extracting unit 25 to extract user data from the received packet, and a data transferring unit 26 to transfer the extracted user data to an application program.
When no errors are detected, the packet error detecting unit 22 sends the received packet to the data extracting unit 25. If an error is detected, the packet error detecting unit 22 disregards the received packet.
Depending on the available buffer space, in which the received packets are buffered, the response packet generating unit 23 sets the maximum number of packets to be sent to the network from the packet sending device 10, and generates a response packet including the set maximum number of packets, the sequence numbers of the packets received to date, and the sequence numbers of the packets to be received in the future.
Accordingly, the packet sending device 10 determines the maximum number of packets that can be sent to the network, based on a response packet, and continuously sends the packets based on a predetermined transmission rate, and under the limits of the determined maximum number of packets.
Operations of the conventional wireless network apparatus described above will be described with reference to FIG. 2.
The packet receiving unit 21 receives a packet sent from the packet sending device 10 S10.
The packet error detecting unit 22 determines whether there are any errors in the received packet S20.
The packet error detecting unit 22 determines whether there are any errors in the received packet through a checksum field of the received packet.
When it is determined that the packet has no errors, the received packet is sent to the data extracting unit 24, which extracts the user data S30. The extracted user data is transferred to an application program by the data transferring unit 26 S40.
However, when the packet error detecting unit 22 detects an error, the received packet is disregarded S50.
Thereafter, the response packet generating unit 23 generates a response packet to inform that there is an error in the received packet, and to include the sequence numbers of the packets received to date and the sequence numbers of the packets to be received in the future S60.
The maximum number of packets is determined by the buffer size of the packet receiving device 10 and this number is included in the response packet, which is used by the packet sending device 10. The generated response packet is sent to the packet sending device 10 through the response packet sending unit 24 S70.
The packet sending device 20 sends packets under the limits so as not to exceed the maximum number of packets, and determines packets to be sent based on the sequence number included in the response packet.
In the wireless network apparatus as described above, a considerable number of packets are buffered in a buffer of a middle node, such as a base station, which connects a wired section and a wireless section.
In other words, when the packet sending device 10 is connected to the middle node by a wire, and the middle node and the packet receiving device 20 are connected wirelessly, the transmission rate of the wireless section would be lower than that of the wired section.
Thus, in view of the time that packets sent to the middle node from the packet sending device 10 are buffered in the middle node, the number of packets sent to the packet receiving device 20 from the middle node must be small. As such, a backlog occurs in the buffer of the base station.
When the packet receiving device 20 described above receives packets from a packet sending devices, packets sent from other packet sending devices cannot be received until the packet receiving device 20 receives all the packets sent from a predetermined packet sending device via the buffer of the base station. Therefore, when no response (packet) to the sent packets is received, the packet sending device may re-send packets through a time-out process.
For this reason, the transmission rate of the packet sending device having later sent packets would be sharply lowered, in comparison of the packet sending device having earlier sent packets.
When a predetermined packet sending device suspends transmission of packets in the course of sending them, the packets already sent are buffered in the base station, thereby causing the problem that other devices cannot send packets.
Japanese Unexamined Patent Publication No. 2004-032218 discloses a communication device base station and a mobile communication terminal capable of preventing a reduction in transmission rate due to packet loss in a wireless link, by maintaining a transmission rate that uses the full estimated bandwidth, rather than by allowing a conventional TCP (transmission control protocol) to halve the transmission rate by allowing packet loss using the available bandwidth estimation (ABE). However, this invention still requires changes in the TCP of all the servers including a sender side and a base station. In other words, when it operates like TCP-Reno, the bandwidth is taken away by TCP-Reno, or it is not applicable although TCP-Vegas, TCP-Westwood, etc. are implemented.